This invention concerns improvements in or relating to a foundry process for cooling and handling foundry sand for use in green sand moulding.
It is the practice to recycle foundry sand after it has been shaken out from the castings. However difficulties arise in both handling and moulding hot sand. In particular, the handling of hot sand creates dust and other pollutants and hot sand has poor flowability, and the moulding characteristics such as strength and permeability are unsatisfactory. For these reasons, and others not mentioned, the foundry sand has to be cooled before it can be recycled, and such cooling requires either special equipment or extensive storage.
It has already been proposed to recycle foundry sand by a process in which hot sand is broken up and mixed with a sufficiently large quantity of fresh or cooled sand so that the resultant mixture has a temperature of below 120.degree. F. Such process is described in the Complete Specification of U.K. Pat. No. 1,266,606 and in use substantial advantages are obtained to overcome the difficulties just mentioned.
In the process of mixing hot and fresh or cooled sand there is a fundamental requirement that the tonnage of foundry sand in the cycle be far greater than the amount of sand required for moulding. For example, if the hot used sand has to be mixed in the rate of 1:3 with fresh or cooled sand, and the casting rate is such as to use 50 ton/hour of moulding sand, the sand in the cycle must be at least 150 ton/hour.
In order to employ such process in and existing plant, the sand handling and treatment plant cannot be simply modified to increase its capacity by three times. Accordingly, the change to such process may incur substantial capital investment and foundry shutdown so that there is a financial deterrent.